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PCC 6803 that flavodoxin expression is not able to fully compensate for
a deletion of the ferredoxin-encoding gene (
Poncelet, Cassier-Chauvat,
Leschelle, Bottin, & Chauvat, 1998
).
4.3.3. IdiABC
Several additional iron-deficiency proteins were identified. Iron-deficiency-
induced protein A was identified in
S. elongatus
PCC 7942 (idiA;
Michel
et al., 1998
). This gene is specific for cyanobacteria and cannot be found
in green algae or higher plants (
Michel & Pistorius, 2004
). The expression
of
idiA
is under the control of the transcriptional activator IdiB (
Michel,
Pistoriusm, & Golden, 2001
), which is induced upon iron starvation but
disappears shortly after iron depletion (
Yousef, Pistorius, & Michel, 2003
).
The transcript of
idiB
is more stable than the transcript of
isiAB
and remains
detectable for more than 10 h after iron depletion (
Yousef et al., 2003
).
Electron microscopic analysis of single PSII particles indicated that IdiA
directly interacts with CP43 and D1 (
Lax et al., 2007
). Thus, a model was
suggested, by which IdiA protects the cytosolically exposed acceptor side of
PSII exposed after phycobilisome degradation (
Nodop et al., 2008
).
However, in the literature, 'IdiA' was also used for the gene product of
slr1295 in
Synechocystis
sp. strain PCC 6803 (
Tölle et al., 2002
). Indeed, the
latter is the closest homologue when the IdiA sequence from
S. elongatus
PCC 7942 (syc1920_d) is used for a search. However, reblast analysis using
the sequence from
Synechocystis
sp. strain PCC 6803 reveals a closer relation
to syc0146_c, which encodes an iron transport system substrate-binding
protein. This is confirmed by the relation to alr1382 from
Anabaena
sp. PCC
7120, which has been annotated as periplasmic iron transport protein FutA
(Stevanovic et al., 2012). Considering these results, the
Synechocystis
IdiA
should be considered as FutA1, the second annotated name of the protein
(
Katoh, Hagino, & Ogawa, 2001
).
IdiB is a helix-turn-helix transcriptional regulator of Crp/Fnr type
(
Michel & Pistorius, 2004
). It regulates not only
idiA
but also other genes
involved in protection against damage caused by iron limitation. In a global
analysis of iron starvation-dependant expression in wild-type
S. elongatus
PCC 7942, an
idiB
-free mutant and a merodiploid mutant with signifi-
cantly reduced expression
idiB
and
idiC
revealed a global function for IdiB.
For example, expression of
irpA
,
irpB
,
somA
(2),
somB
(1),
idi
A, as well as
genes coding for an acetate kinase (ackA) and for phosphoglycerate mutase
(pgma). The latter two are both proposed to function in acetate-phosphate
metabolism (
Nodop et al., 2008
) and thus, the IdiB-dependant regulation of
